Underground utility strikes during excavation operations can be dangerous and costly. The Common Ground Alliance (CGA) reported 203,000 such strikes in the U.S. and Canada during 2021, which resulted in damages of $30 billion and in some cases, worker deaths. Contractors can protect workers and avoid damaging vital water, sewer, electric and telecommunications lines by planning ahead and following best practices for digging near utilities.

The CGA identified three major causes of utility damage: failure to notify the utilities before digging, failure to maintain sufficient distance between the digging equipment and the buried lines and inaccurate mapping or incomplete records of utility locations. In a recent United Rentals webinar, Joe Wise, region customer training manager with the Trench Safety group, offered the following suggestions for avoiding these pitfalls.

1. Contact all utilities before you dig

Before you dig, it’s essential to locate underground utilities. To do so, call 811, the “call before you dig” phone number, several days in advance. In 50 U.S. states and five Canadian provinces, calling 811 will provide you with information about the approximate location of public utilities in that area and serve as your notification to those utilities that you intend to excavate there. Note that if the excavation could impact private lines or private utility companies, you must call those companies directly.

After calling 811, you need to wait, typically for a few days, before starting work. The exact amount of time depends on the regulations of the state or province.

It’s a good idea to have a record of who made the calls to 811 or other utilities and what information was provided to you. Compliance officers that come to check your site may ask for these details.

2. Have a competent person direct or conduct onsite utility location

Once the utility has indicated the general location of underground utilities in the area, a designated competent person should be in charge of pinpointing their exact location. This is usually done using electromagnetic induction equipment and/or ground penetrating radar.

Check for features such as manholes and vent stacks that may indicate the presence of a utility. As-built drawings or maps may help identify the location of the utility as well.

Mark the area with colored flags or lines for different types of utilities according to your jurisdiction’s requirements.

3. Evaluate the site conditions before choosing a protective system

Protective systems for trenches around utilities can include vertical hydraulic shores, hydraulic walers, modular aluminum boxes, trench shields, manhole braces and G3 (sheeting) systems.

To reduce the risk of cave-ins, when choosing a trench protective system the competent person should evaluate the soil along the entire length of the excavation rather than taking samples at just site. The system design should take into account factors such as the impact from disturbed adjacent soils and any surcharges from heavy equipment or spoil piles in the adjacent area. To determine the adjacent area, measure the depth of the excavation and then measure the same distance out from the edge of the excavation.

Assemble the protective system you choose according to the manufacturer’s directions and follow the manufacturer’s tabulated data and notes. You may need to reduce the limits listed in the tab data due to site conditions. Consult a professional engineer if you have any doubts about how a particular system will work on your site.

4. Support any exposed utilities

If a pipe or crossing utilities will be exposed during the excavation, plan how you’ll support them. Exposed, unsupported pipes may break or suffer damage if the soil collapses.

5. Use soft digging within the tolerance zone

Contractors may not use backhoes, excavators or any other mechanical device to dig within the tolerance zone, which is the area around the paint or flags that mark the utility. The width of this zone varies by jurisdiction.

The soft digging methods permitted within this area include hand digging and potholing. Potholing is the use of vacuum excavation with water or air to create small holes above the utility lines to expose them.

6. Know what to do if a strike occurs

Underground utility strikes can happen despite best efforts. Resulting damage can include line breaks and damage to the line’s protective covering, lateral supports or housing.

If an electric line or a pipe carrying natural gas or another hazardous substance is damaged, OSHA requires the contractor to call 911 immediately. The next step is to call the 811 line and/or the utility owner to report the strike.

Document the damage with date- and time-stamped photos. Before you backfill the area around the utility line, make sure the line has been inspected by the utility owner.

Digging near underground utilities poses the double challenge of keeping workers safe in the trenches while avoiding disruptions to the essential services the utilities provide. Following these tips can help contractors do both successfully.

Contact the United Rentals Trench Safety team for assistance with your next excavation, including help designing a custom protective system.